Adaptive power regulation of LED driver module for emergency lighting

ABSTRACT

An adaptive power regulation converter for battery powered emergency lighting LED driver is disclosed. The power feedback and power compensation circuits regulate the output power to LED strings and provides tighten regulated constant power and constant lumens for emergency light during power out time. The adaptive power regulation converter can be used for a great range of LED strings.

BACKGROUND OF INVENTION 1. Field of the Invention

The invention relates generally to power regulation and more particularly to precise and adaptive power regulation of LED driver modules and methods for emergency lighting applications.

2. Description of the Related Art

Traditionally, a switching mode power supply is a voltage regulated converter to maintain constant voltage at the output load or a current regulated converter to maintain constant current at the output load. For emergency light systems the load is the lighting output. Most of today's emergency light systems use LEDs as lighting output for best efficiency. It is well known that LED consumes much less power than any other light sources. Since emergency power lighting is powered by back up battery in an emergency event, consuming as little power as possible is critical to extend the life of the light output. However, the government regulation for emergency lighting requires that in an emergency event, the LEDs light output need to provide a certain minimum lumens or brightness for a minimum period of 90 minutes using the backup battery power for the emergency lighting. The best and most optimal solution to meet the above requirement is to supply constant power to the LEDs from the back up battery during the emergency event. However, providing the sufficient minimum lumens for the required period of at least ninety minutes for a wide range of LED strings and different manufacturers of LEDs by using a backup battery system is a great challenge.

Voltage drops on different LED strings is based on the numbers of LED cells in the series of the LED strings and on the type of LED used in the LED strings. The voltage-current (V-I) characteristic of an LED is not linear. A constant voltage converter can be only used for one particular type of LED or LED strings' load. If a different type or a different make of LEDs are used, then the constant voltage converter is insufficiently able to meet the requirements.

The emergency LED light's lumens is according to the battery capacity used, in terms of power. A conventional emergency LED driver is a current-regulated converter which deliver a constant current over a range of load voltages. This results in LED light's lumens gradually increasing from using more LEDs or gradually decreasing from using less LEDs in the emergency lighting system. Using constant current can also results in battery power not being completely used up during the ninety minutes if the lighting system uses less LEDs. This results in wasted left over capacity of the backup battery and is not cost effective and not optimal. On the other hand, if the same lightning system uses more LEDs, the power from back up battery may not last the required minimum 90 minutes of required output lumens. This results in the failure to meet the safety standards and safety testing (e.g., by UL). Therefore, the best solution is to use a constant power to drive the LEDs output instead of using constant voltage or constant current type. Constant power will solve the issues described above.

In the market today, there are companies manufacturing constant power LEDs driver circuit for the emergency lighting system. As an example, a prior art invention which was patented by this inventor, titled “Constant Power Supply for LED Emergency Lighting using Smart Output Resetting Circuit for no Load Condition” and disclosed in U.S. Pat. No. 9,398,649, focuses on inherent property of constant power in discontinuous conducted mode (DCM) flyback converter. In that invention, the primary side power is regulated without feedback from secondary side, which results in rough power regulation. U.S. Pat. No. 9,398,649 teaches that the output power is 0.5*Lp*(Ip^2)*fsw*η, where Lp is transformer primary winding inductance, Ip is the peak primary inductor's current, fsw is flyback converter's switching frequency and q is converter's efficiency. Assuming Lp, fsw and η are constant, then regulating Ip can regulate output power. However, in the real world, the transformer primary winding inductance's error tolerance is normally 15% or more. In addition, the Ip sensing resistor could have a 1% error tolerance. The frequency is set by RC (resistor-capacitor) network. It is a common knowledge for those skilled in the art that the RC error could be up to 6%. In U.S. Pat. No. 9,398,649, if the converter efficiency is the same for all unit, the power regulation error is affected by the errors of Lp, Ip, and fsw. The actual output power is Po=0.5*(a*Lp)*((b*IP)^2)*(c*fsw)*η, where a, b and c are variables. There are factors of these errors of each component. The power error is δP%=a*(b^2)*c−1.

As an example, if the variable a is 1.15, variable b is 1.01 and variable c is 1.06, then the power regulation error is 24.35%. If the variable a is 0.85, variable b is 0.99 and variable c is 0.94, then power regulation error is −21.69%. Thus, in this example, the power regulation error is in the range of −21.69% to 24.35%. Due to the wide error range, this means that in mass production, manual adjustment of each driver's output power is needed and that significantly increases product cost.

The prior art (U.S. Pat. No. 9,398,649) methods for achieving constant power is limited by poor regulation and therefore the need to do manual tuning of each part during mass production which increases cost. In addition, this prior art teachings are also limited to one topology which is the discontinuous conducted mode flyback converter.

Therefore, there is a need for new and improved constant power regulation systems and methods for emergency lighting applications that address and solve the problems associated with the prior art described above.

The aspects or the problems and the associated solutions presented in this section could be or could have been pursued; they are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches presented in this section qualify as prior art merely by virtue of their presence in this section of the application.

BRIEF INVENTION SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter.

As a background, the regular pulse width modulation integrated circuits (PWM Chip, PWM IC, PWM IC chip) are configured to do output voltage or current regulation of a power converter. This invention teaches the concept of using a regular low cost readily available PWM IC and adapt it to do power feedback and output power regulation instead.

In an aspect of the invention, three variations of converter for LED drivers with power sampling, power feedback and power compensation loop are provided. Each uses an analog multiplier which generates power sample signal from samplings of output current and output voltage. The analog multiplier multiplies the two independent components of the output, i.e., output current sampling and output voltage sampling. The product of these two independent components is the output power sampling, in the form of a voltage signal, which, after being scaled down to provide power feedback signal, goes through a power compensation network. The scaled down power sample signal is compared to a precise reference voltage which could be, but is not limited to, an internal reference voltage inside the PWM Chip. If a difference is detected, a power error signal is generated. This power error signal inputs through outer loop and enters the first input of a comparator. In addition, primary current feedback goes through the inner loop to the second input of the same comparator. This is used to control the pulse width of the PWM Chip. These inner loop and outer loop signals are used to generate a PWM signal which turns on and turns off the power MOSFET to achieve a very tight power regulation, for example, but not limited to, a +/−3% of power regulation. This provides a very tight and better adaptive power regulation. The basic concept of using the PWM Chip is well known to those skilled in the art of switch mode power conversion. This invention is to use the same PWM Chip and its internal circuitry to do power feedback and output power regulation instead of the regular output voltage or current regulation.

In another aspect, the power regulated LED driver circuit disclosed herein is versatile because it is not limited to a few topologies and to discontinuous topologies. In fact, the teachings of this invention can be used in Forward, Boost, Buck, Buck-Boost and Flyback topologies with continuous and discontinuous mode, etc.

The above aspects or examples and advantages, as well as other aspects or examples and advantages, will become apparent from the ensuing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For exemplification purposes, and not for limitation purposes, aspects, embodiments or examples of the invention are illustrated in the figures of the accompanying drawings, in which:

FIG. 1 illustrates a block diagram for a power regulation LED driver circuit, according to an embodiment.

FIG. 2 illustrates a schematic for two switchers Forward regulated power LED driver circuit, according to an embodiment.

FIG. 2A shows additional detail of Circuit 1 of FIGS. 2, 3 and 4, namely internal detail of an exemplary existing IC chip shown in FIGS. 2, 3 and 4 as U1, and detail of the connection between U1 and Op Amp U2A, according to an aspect.

FIG. 3A shows internal detail of a prior art IC chip shown in FIG. 3 as U4.

FIG. 3 illustrates a schematic for boost regulated power LED driver circuit, according to an embodiment.

FIG. 4 illustrates a schematic for Flyback regulated power LED driver circuit, according to an embodiment.

DETAILED DESCRIPTION

What follows is a description of various aspects, embodiments and/or examples in which the invention may be practiced. Reference will be made to the attached drawings, and the information included in the drawings is part of this detailed description. The aspects, embodiments and/or examples described herein are presented for exemplification purposes, and not for limitation purposes. It should be understood that structural and/or logical modifications could be made by someone of ordinary skills in the art without departing from the scope of the invention. Therefore, the scope of the invention is defined by the accompanying claims and their equivalents.

It should be understood that, for clarity of the drawings and of the specification, some or all details about some structural components or steps that are known in the art are not shown or described if they are not necessary for the invention to be understood by one of ordinary skills in the art. Also, as it should be recognized by one of ordinary skills in the art, throughout this description, “u” is used in place of “μ” to represent the prefix micro when referring to measurement units.

FIG. 1 illustrates a block diagram for a power regulation LED driver circuit, according to an embodiment. The structure and function of the elements depicted in FIG. 1 will be readily apparent from the ensuing description referring to FIGS. 2-4. As it will be described in more detail hereinafter, the power regulated LED driver circuit disclosed herein provides constant power to LED strings using power feedback and power compensation network for battery backup powered emergency lighting system. The adaptive power converters described herein use power feedback to adjust power to the LED strings and provides a predetermined constant power and a constant lumen during all lighting backup periods. The adaptive power converters described herein will meet the regulatory requirement of at least 90 minutes of run time while maintaining the minimum lumens requirement in an emergency event. It can be used on a wide variety of LEDs types, and LED strings. The adaptive power converters described herein can be mass produced at a lower cost as it does not require manual tuning of each part during mass production.

FIG. 2 illustrates a schematic of a two switchers Forward regulated power LED driver circuit, according to an embodiment. This exemplary embodiment may be configured as a 5 Watts two switchers forward LED Driver with an output voltage range of 14V˜58V.

As shown, Circuit 1 of the schematic diagram shown in FIG. 2 may be an analog multiplier circuit for power sensing and power sampling. This analog multiplier circuit may be implemented by using an analog multiplier device, including, but not limited to MAX4210E, or other similar devices that may be constructed by using discreet components and/or integrated circuits (IC). In this example, the analog multiplier device MAX4210E multiplies the samples of output voltage and output current to generate an analog voltage proportional to the output power consumed by the LED load.

Circuit 1 of FIG. 2 is the power signal generator circuit and comprises of the following components: R15 (e.g., 10KΩ), R16 (e.g., 1KΩ), R17 (e.g., 150KΩ), R18 (e.g., 150KΩ), R19 (e.g., 140KΩ), R20 (e.g., 10KΩ), R21 (e.g., 100KΩ), R22 (e.g., 102KΩ), DZ1 (e.g., 5V), U1 (e.g., MAX4210E), U2A (e.g., LM324), Q1 (e.g., MOSFET), C1 (e.g., 820 uF), C3 (e.g., 0.1 uF), C4 (e.g., 0.01 uF) and C8 (e.g., 47 pF). R15 and DZ1 provide 5V linear regulated auxiliary voltage (Vcc) for U1 (e.g., MAX4210E). U1 operates in the positive quadrant to provide positive voltage proportional to the output power with power sense amplifier gain (e.g., 25 times power gain of the MAX4210E). The R19 (140KΩ) and R20 (10KΩ) resistor divide senses and samples output voltage. The sampling voltage Vs=Vo*R20/(R20+R19) scaled down Vo from 14V˜58V to 0.667V˜3.867V. The sampling voltage inputs to pin 2 “IN” of U1 (e.g., MAX4210E). The output current sensing signal in the form of voltage on R30 and R31 goes through R16 and filtered by C8 to pin 3 “+” input of U2A. This output current sensing voltage is then converted into a current by the Op Amp U2A (e.g., LM324).

A current mirror which comprises MOSFET Q1, resistor R18 (150Ω) and resistor R17 (150Ω) then converts it to a smaller voltage inputs to a differential input Pin 5 (“RS+”) and Pin 7 (“RS−”) of U1. For 5 W and 58V output LED driver, this LED output current from J2 Pin 2 (“LED−”) flowing through R30 (0.6 ohms) and R31 (0.6 ohms) is converted to voltage which is V_RS=(Po*(R30//R31))/Vo. Po is the output power provided to output LED load. Vo is the output voltage which is on J2, Pin 1 (“LED−”). In this example, this current converted voltage V_RS is 0.026V. In another example, for 5 W and 14V output LED driver this current converted voltage V_RS is 0.15V. In this case, the maximum input voltage of “RS+” and “RS−” is 0.15V. These R18 and R17 values are chosen for this maximum input voltage. The sampling power full scale is 2.5V. Ps=Gp*Vs*V_RS=25*0.667*0.15=2.5(V).

J1 is connected to the battery, which supplies the power to the invention. The auxiliary power supply Vcc (Pin 4 of U1) is 5V and is derived from J1 regulated by DZ1. The Op Amp output has enough headroom for power output with 5 volts Vcc. R21 (100K Ω) and R22 (10K Ω) is a voltage divider to scale down power sampling output, and thus provide power feedback, for next stage of power compensation circuit of Circuit 2. The resistor divider of R21 and R22 sets the pre-determined output power.

As shown in this embodiment, Circuit 2 is a PWM circuit configured to do power regulation. The basic PWM circuit is well known to those skilled in the art of Switching Mode Power Supply (SMPS). In the normal application of PWM circuits, the voltage or current are being regulated. There is no literature or product in the market that uses the PWM circuit to do power regulation. The novel invention here teaches the use a regular PWM circuit to handle power regulation to the output loads.

Circuit 2 of FIG. 2. shows an embodiment of the invention as a two-switcher Forward power regulator comprising components: R23 (e.g., 24.9KΩ), R25 (e.g., 20KΩ), R30 (e.g., 0.6Ω), R31 (e.g., 0.6Ω), D1, D2, D5 (e.g., CMHD4448), D6 (e.g., CMHD4448), U4 (e.g., LM5015), C5 (e.g., 0.1 uF), C6 (e.g., 2200 pF), C2 (e.g., 150 pF), C9 (e.g., 0.01 uF), C11 (e.g., 0.1 uF), C12 (e.g., 330 uF), C15 (e.g., 0.22 uF), T1, L1 (e.g., 0.77 mH) and J2. It should be apparent that the role of Circuit 2 in FIG. 2 is to drive output LED strings by providing regulated power. The R23 (24.9KΩ), C6 (2.2 nF) and C2 (150 pF) form an error amplifier compensation circuit. The power sampling signal input from R21 and R22 goes into Pin 3 “FB”. At the same time, the output of Pin 4 “COMP” after passing through the RC Network (e.g. C2, C6 and R23) also goes into pin 3 “FB” of the two switcher Forward regulator U4 (e.g., LM5015). These provide circuit stabilization.

In other words, the circuit network is stabilized and compensated by the external RC network and a built-in error amplifier inside U4 for converter operation. In this example, the output signal of error amplifier inside the PWM is a power error signal. This power error signal is called the outer loop feedback signal of the power regulator. In this example, the PWM U4 has a primary current feedback circuit. This primary current feedback signal is called the inner loop signal. The power error signal (generated from output current and output voltage to regulate output power by means of adjusting primary current pulse width) and primary current feedback signal are the inputs to a built-in PWM comparator inside U4 to generate pulse width modulation (PWM) signal to control the two built in MOSFET switchers to turn on and off. The turn on and turn off duration is defined by the PWM pulse width to achieve a +/−3% (or better) of tighter and better, adaptive power regulation. R25 (20K Ω) resistor connects to pin 2 “RT” and it programs oscillation frequency to 300 kHz, for example. C9 (0.01 uF) capacitor, sets the soft start delay time for example. C15 (0.22 uF) ceramic capacitor, is a bypass capacitor of Vcc of U4 for example.

Two clamp diodes D5, D6 are used to clamp the internal MOSFETs voltage to the input battery voltage. Therefore, there is no need for a snub circuit for the switching components. The C5 (0.1 uF) is a high side bootstrap bias capacitor. T1 is a step up Forward power transformer. T1 delivers primary power to the secondary LED load. D1 is output rectifier and D2 is the free wheel diode. D1 and D2 are Schottky diodes or fast recovery diodes with low forward drop voltage. The high frequency filter capacitor C11, and the output filter capacitors C12 attenuate output voltage ripple and noise spike. The output inductor L1 is selected to ensure Forward converter operates under continuous conducted mode (CCM). R30 (0.6Ω) and R31 (0.6Ω) are output LED current sensing resistors. The voltage on R30 and R31 provides feedback to the multiplier shown as Circuit 1. J2, a connector connects the converter to external LED strings.

For a Forward converter, it is known to those skilled in the art that: Po=Vo*Io  (1) Vo=Vin*D/n  (2)

where D is duty cycle, n is turns ratio Np/Ns where Ns is the primary turns and Ns is the secondary turns of the transformer (T1). In order to achieve the maximum output voltage range, the maximum and the minimum duty cycle must be properly selected based on the turn ratio of the transformer. For example, for a maximum output voltage of 58V, when minimum input voltage is 8.4V, the turns ratio should be selected to be 1:14, then, the maximum duty cycle is 0.49. As another example, when the output voltage is 14V and input voltage is 12V and with the same turn ratio of 1:14, the minimum duty cycle is 0.056. Also, for the Forward converter, it is also known to those skilled in the art that, Io=Iin*D*n  (3)

Replace (2) and (3) to (1) Po=(Vin*D/n)*(Iin*D*n)=Vin*Iin*D^2  (4)

From equation (4) above, the output power is determined by input voltage Vin, input current Iin and duty cycle D. Thus, by controlling duty cycle D by power feedback, output power Po can be regulated.

As an example, for Circuit 1 of two switcher Forward converter, the maximum output power of the converter will correspond to a 2.5V on Pout (Pin 8) of U1. This is the power sampling voltage. In other words, the scaling on Pin 8 of U1 is such that a 2.5V on Pin 8 will make the converter deliver the maximum output power which is 5 watts in this example.

The voltage at Pin 3 of U4 (FB) will scale down to 1.26V by using 100K ohms as R21 and using 102K ohms as R22. This 1.26V on Pin 3 of U4 is the power feedback signal inputs. This Pin 3 of U4 (“FB” pin) is connected to the inverting input of the PWM's internal error amplifier. The non-inverting input of the PWM's internal error amplifier is connected to a 1.26V reference voltage as an example. The PWM's internal high gain error amplifier generates an error signal proportional to the difference between the regulated output power on Pin 3 of U4 “FB” and the reference voltage. The output of the error amplifier is connected to the Pin 4 of U4 “COMP” pin where is a Type II network of loop compensation formed by C6, C2 and R23. This network creates a pole at the origin that rolls off the high DC gain of the amplifier, which is necessary to accurately regulate the output power. A zero provides phase boost near the open loop unity gain frequency, and a high frequency pole attenuates switching noise.

The internal PWM current comparator compares the primary current sense signal on the internal current sensor resistor to a referenced current level (determined by the power error signal) and the current error signal is used to change the pulse width.

If the output power is less than 5 watts (in this example 5W is the set/specified power of the LED load), then the error signal on Pin 4 (COMP) of U4 is less than the internal reference voltage. In this case, the output of internal error amplifier goes more positive and increases the pulse width of the PWM and increasing the output power to achieve the power regulation, and vice versa.

FIG. 3 illustrates yet another embodiment of an alternate implementation of the invention. The schematic of FIG. 3 is a boost regulated power LED driver circuit, according to an embodiment. This exemplary embodiment may be configured as a 12 Watts boost regulated power LED driver with an output voltage range of 14V˜58V.

It should be observed that Circuit 1 in FIG. 3 is the same as in FIG. 2, and, as such, its description when referring to FIG. 2 above is incorporated herein by reference.

Circuit 2 in FIG. 3 shows a boost converter PWM implementation of the power regulation. The following example is familiar to those skilled in the art of SNIPS, except that in this invention the boost circuit is used to do power regulation instead of voltage or current regulation. Circuit 2 of FIG. 3 comprises components: R21, R22, R23, R27, R30, R31, R33, R34, R35, R36, R37 D2, U4, C2, C11, C12, L1, Q6, and J2. It should be apparent that the role of Circuit 2 in FIG. 3 is similar to any PWM circuit, except that it is to drive output LED strings by providing regulated power. The R23 (40K Ω) and C2 (2.2 nF) form an error amplifier compensation circuit and is connected to PIN 2 (COMP) of U4. The power sampling signal input from R21 and R22 goes into PIN 3 (FB) of the PWM Chip U4 (e.g., LM3478).

Circuit 2 of FIG. 3 is stabilized and compensated by a RC network (R23 and C2) and built-in error amplifier of U4 for converter operation. The output signal of the compensation network is a power error signal.

A primary current feedback circuit is from the resistors network (R33 to R37) to PIN 1 (Isen) of U4. The power error signal together with the primary current signal generates the pulse width modulation inside U4. This PWM signal is used to achieve the tight regulation of +/−3% of the power output which is a far more superior power regulation than any similar product in the market.

R27 (40 k-ohm) is connected to PIN 7 of U4 and sets the switching frequency of 400 Khz for the boost converter.

Q6 is a power MOSFET connected to PIN 6 (DR) of U4 which is the driver port. PIN 6 of U4 controls the turning on and off of Q6. This turning on and off of Q6 enables the output power to be regulated.

L1 is a boost inductor. It is used to store and deliver power to the output LED loads. D2 is the output diode. D2 is used to deliver an output voltage that is higher than the input voltage. C11 and C12 are used to filter out high frequency noise and low frequency ripple.

R30 and R31 is the output current sensor resistor. They are used to provide feedback to the power multiplier in Circuit 1. J2 is the output connector

It is well known to those skilled in the art that for a boost converter: Ro=Vo/Io  (2), Ro is the output impedance, Vo is the output voltage and Io is the output current. Vo=Vin/(1−D)  (3), Vo is the output voltage, Vin is the input battery voltage.

where D is duty cycle. For maximum output voltage range, the maximum and minimum duty cycle and turns ratio must be calculated. For example, for maximum output voltage of 58V (Vo), when minimum input voltage is 8.4V (Vin), then the maximum duty cycle D is 0.855. When the output voltage is 14V, and input voltage is 12V the minimum duty cycle is 0.143. The duty cycle should be within a practical range for proper operation. It is between 1 and 0. Io=Iin*(1−D)  (4)

Replace (3) and (4) to (1) the Rin=[Vo*(1−D)]/[Io/(1−D)]=(Vo/Io)*(1−D)^2  (5)

Where Vo/Io=Ro in (5) and manipulate (5) become Rin=Ro*(1−D)^2  (6)

(6) shows the load resistance Ro is reflected to input Rin by (1−D)^2. Input power can express Pin=(Vin^2)/Rin  (7)

From (6), (7) uses duty cycle D can change Rin leads to change input power. Po=Pin−Ploss  (8)

The above equations (1-8) proved that controlling the duty cycle (D) by the power feedback network, we can regulate the output power Po.

As an example, U4 (e.g., LM3478) device is a fixed frequency, Pulse Width Modulated (PWM) current mode controller integrated circuit chip. The inductor's peak current through the external MOSFET is sensed through an external sense resistor R33-R37 (0.053). The voltage across current resistor is fed into the ISEN pin. This voltage is fed into the positive input of the PWM comparator. The output power sampling is through an external feedback resistor divider R21 and R22. This signal is fed into the error amplifier negative input which is the feedback pin, Pin 3 of U4 (FB).

U4 (a PWM IC chip) is used to perform the function of power regulation and voltage boosting based on the inputs it receives from Circuit 1 and inputs from the rest of the network shown in Circuit 2. Essentially, FIG. 3 shows how to use a prior art PWM boost circuit to work as a power regulated circuit.

FIG. 4 illustrates a schematic for Flyback regulated power LED driver circuit, according to an embodiment. This exemplary embodiment may be configured as a 15 Watts flyback regulated power LED driver with an output voltage range of 10V˜58V.

It should be observed that Circuit 1 in FIG. 4 is the same as in FIG. 2, and, as such, its description when referring to FIG. 2 above is incorporated herein by reference.

It should be noted that Circuit 2 in all FIGS. 2, 3, 4 are fixed frequency PWM controller circuits for DC-DC converter. The PWM controller in all three circuits also provides full compensated Error Amplifier, current sense comparator and a totem pole output driver.

The PWM portion of Circuit 2 in FIG. 4 comprises components: R21, R22, R23, R24, R25, R26, R27, D1, U4, Q5, C2, C5, C6, C7 and C15. It should be apparent that the role of Circuit 2 in FIG. 4 is to drive output LED strings by providing regulated power. As an example, the R24 (1K Ω), C2 (0.1 uF), and R23 (100K Ω) form an error amplifier compensation circuit. As shown in FIG. 4, the input to Pin 2 (“IN”) of U1 is the output voltage sampling which is Vs. Vs is derived from Vo. The power sampling signal output from Pin 8 (“Pout”) of U1 passes through R21 to connect to the RC network (C2 and R23). Circuit 2 of FIG. 4 is stabilized compensated by the RC network and the built-in error amplifier of U4 (e.g., UC3845B) for the converter operation. The power compensation network consists of R24, R23 and C2.

The output signal of the power compensation network is a power error signal. This power error signal is connected to PIN 1 (COMP) of U4.

The primary current feedback signal is generated by the resistor networks (R33 to R37) and through R29 is connected to PIN 3 (CS) of U4.

The power error signal and primary current feedback are connected to PIN 3 (CS) of U4. Internal to the PWM chip, these signals on PIN 1 (COMP) and PIN 3 (CS) are the inputs of the built-in comparator used to generate pulse width modulation (PWM) signal on PIN 6 (OUT) of U4. The internal workings of the PWM IC chip is a well-known prior art and is therefore not fully elaborated here. The output of the PWM IC chip (PIN 6) which is a modulated pulse width signal turns on and turns off the power MOSFET (Q6) to achieve a tight power regulation of +/−3% and provide a better adaptive power regulation.

As an example, C6 (1000 pF) and R27 (10K Ω) resistor connected to pin 4 and pin 8 of U4 are used to set the oscillation frequency of the flyback converter. The oscillation frequency is 1.72/(R27*C6).

C7 (0.01 uF) is a bypass capacitor for the reference voltage output which is PIN 8 (Vref) of U4.

C15 (1 uF), a ceramic capacitor is used as a bypass capacitor for Vcc which is PIN 7 of U4.

The soft start and primary inductance current sense voltage clamping circuit consists of D1, C5, R25, R26 and Q5.

As an example, C5 (1 uF) capacitor, R25 (100 k Ω, R26 (34K Ω) resistors and a PNP small signal transistor, Q5, form the soft-start circuit and the primary inductance current sense voltage clamping circuit.

The clamping circuit includes resistors R25 and R26. The clamping voltage is (R26/(R26+R25))*1V. In this embodiment, the clamping circuit clamps peak voltage in current of sensor resistor from 1 V to 0.25 V by selecting R25 and R26 value. It greatly reduces power loss on current sensing resistor.

Circuit 2 of schematic diagram shown in FIG. 4 is a Flyback adaptive converter to implement the regulated constant power LED driver.

The Flyback converter comprises components: R28, R29, R33, R34, R35, R36, R37, R32, R30, R31, D2, T1, Q6, C9, C10, C11, C12 and J2. As an example, the R28 (4.3Ω) and C9 (2200 pF) provide snubbing on the primary winding of T1 to attenuate the voltage spike generated by transformer's leakage inductance on primary winding of T1. Q6 is power switching NMOSFET controlled by output PIN 6 (OUT) of U4. The R33, R34, R35, R36 and R37 resistor network is the primary inductance current sensing resistors. All the resistors (R33 to R37) selected in this example is 0.24 Ω to achieve a 15 W constant power output. It should be understood that different resistors' value is needed for different output power.

T1 is a Flyback power transformer. T1 delivers primary power to secondary LED load. The primary and secondary windings in the Flyback transformer (T1) conduct current at different times. The Flyback transformer actually operates as an inductor when the primary winding is conducting. The primary to secondary ampere-turns ratio is conserved in this conducting mode. The voltage transformation is taking place between primary and secondary windings of T1, whereby the secondary voltage is reflected to the primary winding during transistor Q6 turn off time.

The power feedback, primary current feedback and power compensation network changes the pulse width to regulate the output power deliverable from primary winding's stored power. The C10 (100 pF) and R32 (475Ω) is the snubber on output diode D2 to attenuate voltage spike generated by transformer leakage inductance on secondary winding of transformer T1.

The output diode D2 is to rectify the output voltage of transformer T1 output. C11 (0.1 uF) and C12 (680 uF) are used to filter high frequency voltage spikes and to filter low frequencies ripples.

R30 (0.2Ω) and R31 (0.2Ω) are output LED current sensing resistors. The voltage on R30 and R31 provides feedback to the multiplier circuit in Circuit 1 of FIG. 4. The C11 (0.1 uF) and C12 (680 uF) are output filter capacitor to smooth the output DC voltage and current. J2 is connector to connect the converter to external LED strings.

The invention has been described with respect to three sample embodiments. Those having skill in the art will recognize that additional embodiments will be within the scope of this invention. The invention is not limited by the description of these sample embodiments, but instead of that defined in accordance with the claims. For example, it can be recognized that one can design, similarly as described herein, modified LED drivers to regulate 5-watt, 7-watt, 10-watt, 12-watt, 15 watts, 20 watts, etc. with operating output voltage from 10V to 58V.

A power feedback closed loop and power compensation technique as disclosed herein results in a tighter regulated constant power converter. Typically, a +/−3% or better power regulation error can be achieve using this novel invention. Further, this novel power control technique tightens the regulated power on output load under various input voltage and output LED load conditions.

Since the constant power LED driver's output current and voltage are variables, they shall not be used for power regulation individually. Therefore, the error signal cannot be taken from output current sampling and output voltage sampling, individually. To regulate output power, the error signal input to error amplifier must be the output power sampling as described herein.

The driver circuits disclosed herein use analog multiplier to multiply two independent components: one of voltage input, which is converted from output current sampling and another of voltage input, which is the output voltage sampling. The product of the two independent components is the output power sampling, in the form of voltage signal. The disclosed circuits then compare the output power sampling value to a reference fixed value inside the PWM for example to generate a power error signal. This power error signal inputs to power feedback loop. The power error signal combining with the primary current feedback signal generates the variable pulse width to regulate the output, as described herein.

Again, the LED driver circuit disclosed herein is versatile and advantageous in that this topology is suitable to two-switch Forward converter, Boost converter and Flyback converter in continuous conducted mode (CCM) or discontinuous conducted mode (DCM) Flyback converter, to mention just a few.

Further, as disclosed herein, the LED driver circuit uses power feedback and power compensation loop to control pulse width modulation (PWM) to achieve precise power regulation. An analog multiplier generates power sample signal from samplings of output current and output voltage for power regulation. This technology can regulate output power within +/−3% and thus automatically results in higher yield in mass production of these type of driver circuits.

The values (or component type or part number) of the circuit components described throughout this disclosure (e.g., R28, 4.3 Ω and C9, 2200 pF) are only examples particular to the examples of circuit configurations disclosed herein. Thus, unless otherwise expressly stated herein, it should be understood that logical deviations from these values and examples may be made while still obtaining similar results.

It may be advantageous to set forth definitions of certain words and phrases used in this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.

Further, as used in this application, “plurality” means two or more. A “set” of items may include one or more of such items. Whether in the written description or the claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of,” respectively, are closed or semi-closed transitional phrases with respect to claims.

If present, use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence or order of one claim element over another or the temporal order in which acts of a method are performed. These terms are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. As used in this application, “and/or” means that the listed items are alternatives, but the alternatives also include any combination of the listed items.

Throughout this description, the aspects, embodiments or examples shown should be considered as exemplars, rather than limitations on the apparatus or procedures disclosed or claimed. Although some of the examples may involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives.

Acts, elements and features discussed only in connection with one aspect, embodiment or example are not intended to be excluded from a similar role(s) in other aspects, embodiments or examples.

Aspects, embodiments or examples of the invention may be described as processes, which are usually depicted using a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may depict the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. With regard to flowcharts, it should be understood that additional and fewer steps may be taken, and the steps as shown may be combined or further refined to achieve the described methods.

If means-plus-function limitations are recited in the claims, the means are not intended to be limited to the means disclosed in this application for performing the recited function, but are intended to cover in scope any equivalent means, known now or later developed, for performing the recited function.

If any presented, the claims directed to a method and/or process should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.

Although aspects, embodiments and/or examples have been illustrated and described herein, someone of ordinary skills in the art will easily detect alternate of the same and/or equivalent variations, which may be capable of achieving the same results, and which may be substituted for the aspects, embodiments and/or examples illustrated and described herein, without departing from the scope of the invention. Therefore, the scope of this application is intended to cover such alternate aspects, embodiments and/or examples. Hence, the scope of the invention is defined by the accompanying claims and their equivalents. Further, each and every claim is incorporated as further disclosure into the specification. 

What is claimed is:
 1. A regulated power LED driver circuit comprising a first circuit electrically connected to a second circuit, the first circuit comprising an analog multiplier and being adapted to generate an output power sampling signal in the form of voltage signal by multiplying sampling of output current and sampling of output voltage of the driver circuit, and a voltage divider that scales down the output power sampling signal, the second circuit comprising a power feedback and power compensation network adapted to receive the scaled-down output power sampling signal from the first circuit, a comparator that generates a power error signal by comparing the scaled-down output power sample signal with a reference voltage, a resistor adapted to provide a primary current feedback signal, a switcher, and a pulse width modulation (PWM) comparator that receives as inputs the power error signal and the primary current feedback signal and generates a modulated pulse width signal and thus controls the switcher's turning on and off, to regulate the output power of the LED driver circuit.
 2. The regulated power LED driver circuit of claim 1 wherein the switcher is a power MOSFET.
 3. The regulated power LED driver circuit of claim 1 wherein the second circuit is adapted to increase pulse width when output power is lower than a set power of an LED load and to decrease the pulse width when the output power is higher than the set power of the LED load.
 4. The regulated power LED driver circuit of claim 1 further comprising one of a transformer and an output inductor.
 5. A regulated power LED driver circuit comprising: an output power sampling circuit comprising an analog multiplier and being adapted to generate an output power sample signal by multiplying samplings of output current and output voltage of the driver circuit; and a power converter circuit comprising a pulse width modulation (PWM) comparator and being electrically connected to the output power sampling circuit, the power converter circuit being adapted to receive the output power sample signal from the output power sampling circuit in the form of voltage signal, generate a power error signal by comparing the output power sample signal with a reference voltage and determine output power level based on the power error signal and a primary current signal.
 6. A method of power regulation of an LED driver circuit, the circuit comprising an analog multiplier electrically connected to a pulse width modulation (PWM) comparator, the method comprising: generating an output power sampling signal in form of voltage signal by multiplying samplings of output current and output voltage of the driver circuit; generating a power error signal by comparing the output power sampling signal with a reference voltage; and determining output power level based on the power error signal and a primary current signal.
 7. The method of claim 6 further comprising using a voltage divider to scale down the output power sampling signal.
 8. The method of claim 7 further comprising using a power compensation network to receive the scaled-down output power sampling signal.
 9. The method of claim 8 further comprising generating a modulated pulse width signal to control a switcher's turning on and off thus regulating the power of the LED driver circuit. 